1. Field of the Invention
The present invention relates to a particulate emission treating apparatus designed to filter and burn particulate emissions (mainly black smoke particles) contained in exhaust gas from a diesel engine used in a construction machine or the like. More particularly, the present invention pertains to a particulate emission treating apparatus which is disposed in the exhaust system of a diesel engine and which employs a honeycomb type ceramic filter to filter and burn particulate emissions.
2. Description of the Related Art
One type of particulate emission treating apparatus has heretofore been known which employs a honeycomb type ceramic filter to filter and burn particulate emissions from a diesel engine used in a construction machine or the like. Such a honeycomb type ceramic filter is disclosed in, for example, "Diesel Particulate Control" in Automotive Engineering, November 1984, pages 63-70, published by the Society of Automotive Engineers Inc. in 1984 and "Diesel motorcar Exhaust Gas and countermeasures therefor" in Machine Research, Vol. 39, No. 10, pages 1103-1104, published by Japan Machinery Institute in 1987. FIG. 1 illustrates a prior art particulate emission treating apparatus incorporating a honeycomb type ceramic filter of the type described above, in which a ceramic filter 5 is accommodated in a casing 3 disposed between exhaust system pipe lines 1a and 1b and surrounded by a cushioning material 7. With this structure, however, the cushioning material 7 thermally expands in the area between the filter 5 and the casing 3 during use, and this makes it difficult to remove the filter 5. When seeking to replace the filter 5, therefore, it is necessary to conduct a troublesome operation in which the filter 5 is removed from the casing 3 by crushing it while pulling it up and then a new filter is fitted surrounded by the cushioning material 7. To overcome this problem, another prior art such as that shown in FIG. 2 has been proposed in which a ceramic filter 5 is accommodated in an integrally formed casing 3a with a cushioning material 7 surrounding it, the ceramic filter 5 being replaceable together with the casing 3a in one unit, which is disposed between exhaust system pipe lines 1c and 1d, without the need to remove the ceramic filter 5 from the casing 3a. This structure cannot, however, be adapted to an arrangement in which a plurality of filters need to be provided, and it is also impossible to form a large ceramic filter because of structural limitations due to the strength of the ceramics. Hence, this type of apparatus cannot be used for an engine having a large displacement volume.